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.Dd $Mdocdate: October 1 2023 $
.Dt EVP_CIPHER_CTX_CTRL 3
.Os
.Sh NAME
.Nm EVP_CIPHER_CTX_ctrl ,
.Nm EVP_CIPHER_CTX_set_padding ,
.Nm EVP_CIPHER_CTX_set_key_length ,
.Nm EVP_CIPHER_CTX_key_length ,
.Nm EVP_CIPHER_key_length ,
.Nm EVP_CIPHER_CTX_iv_length ,
.Nm EVP_CIPHER_iv_length ,
.Nm EVP_CIPHER_CTX_set_iv ,
.Nm EVP_CIPHER_CTX_get_iv
.Nd configure EVP cipher contexts
.Sh SYNOPSIS
.In openssl/evp.h
.Ft int
.Fo EVP_CIPHER_CTX_ctrl
.Fa "EVP_CIPHER_CTX *ctx"
.Fa "int type"
.Fa "int arg"
.Fa "void *ptr"
.Fc
.Ft int
.Fo EVP_CIPHER_CTX_set_padding
.Fa "EVP_CIPHER_CTX *x"
.Fa "int padding"
.Fc
.Ft int
.Fo EVP_CIPHER_CTX_set_key_length
.Fa "EVP_CIPHER_CTX *x"
.Fa "int keylen"
.Fc
.Ft int
.Fo EVP_CIPHER_CTX_key_length
.Fa "const EVP_CIPHER_CTX *ctx"
.Fc
.Ft int
.Fo EVP_CIPHER_key_length
.Fa "const EVP_CIPHER *e"
.Fc
.Ft int
.Fo EVP_CIPHER_CTX_iv_length
.Fa "const EVP_CIPHER_CTX *ctx"
.Fc
.Ft int
.Fo EVP_CIPHER_iv_length
.Fa "const EVP_CIPHER *e"
.Fc
.Ft int
.Fo EVP_CIPHER_CTX_set_iv
.Fa "EVP_CIPHER_CTX *ctx"
.Fa "const unsigned char *iv"
.Fa "size_t len"
.Fc
.Ft int
.Fo EVP_CIPHER_CTX_get_iv
.Fa "const EVP_CIPHER_CTX *ctx"
.Fa "unsigned char *iv"
.Fa "size_t len"
.Fc
.Sh DESCRIPTION
.Fn EVP_CIPHER_CTX_ctrl
allows various cipher specific parameters to be determined and set.
Currently only the RC2 effective key length can be set.
.Pp
.Fn EVP_CIPHER_CTX_set_padding
enables or disables padding.
This function should be called after the context is set up for
encryption or decryption with
.Xr EVP_EncryptInit_ex 3 ,
.Xr EVP_DecryptInit_ex 3 ,
or
.Xr EVP_CipherInit_ex 3 .
By default encryption operations are padded using standard block padding
and the padding is checked and removed when decrypting.
If the
.Fa padding
parameter is zero, then no padding is performed, the total amount of data
encrypted or decrypted must then be a multiple of the block size or an
error will occur.
.Pp
.Fn EVP_CIPHER_CTX_set_key_length
sets the key length of the cipher ctx.
If the cipher is a fixed length cipher, then attempting to set the key
length to any value other than the fixed value is an error.
.Pp
.Fn EVP_CIPHER_CTX_key_length
and
.Fn EVP_CIPHER_key_length
return the key length of a cipher when passed an
.Vt EVP_CIPHER_CTX
or
.Vt EVP_CIPHER
structure.
The constant
.Dv EVP_MAX_KEY_LENGTH
is the maximum key length for all ciphers.
Note: although
.Fn EVP_CIPHER_key_length
is fixed for a given cipher, the value of
.Fn EVP_CIPHER_CTX_key_length
may be different for variable key length ciphers.
.Pp
.Fn EVP_CIPHER_CTX_iv_length
and
.Fn EVP_CIPHER_iv_length
return the IV length of a cipher when passed an
.Vt EVP_CIPHER_CTX
or
.Vt EVP_CIPHER .
They will return zero if the cipher does not use an IV.
.Fn EVP_CIPHER_CTX_iv_length
can fail and return \-1.
The constant
.Dv EVP_MAX_IV_LENGTH
is the maximum IV length for all ciphers.
.Pp
.Fn EVP_CIPHER_CTX_set_iv
and
.Fn EVP_CIPHER_CTX_get_iv
set and retrieve the IV for an
.Vt EVP_CIPHER_CTX ,
respectively.
In both cases, the specified IV length must exactly equal the expected
IV length for the context as returned by
.Fn EVP_CIPHER_CTX_iv_length .
.Sh RETURN VALUES
.Fn EVP_CIPHER_CTX_ctrl
usually returns 1 for success, 0 for failure, or \-1 if the
.Fa type
is not supported by the
.Fa ctx ,
but there may be exceptions for some
.Fa type
arguments.
.Pp
.Fn EVP_CIPHER_CTX_set_padding
always returns 1.
.Pp
.Fn EVP_CIPHER_CTX_set_key_length ,
.Fn EVP_CIPHER_CTX_set_iv ,
and
.Fn EVP_CIPHER_CTX_get_iv
return 1 for success or 0 for failure.
.Pp
.Fn EVP_CIPHER_CTX_key_length
and
.Fn EVP_CIPHER_key_length
return the key length.
.Pp
.Fn EVP_CIPHER_CTX_iv_length
and
.Fn EVP_CIPHER_iv_length
return the IV length or zero if the cipher does not use an IV.
.Fn EVP_CIPHER_CTX_iv_length
can fail and return \-1.
.Sh SEE ALSO
.Xr evp 3 ,
.Xr EVP_CIPHER_nid 3 ,
.Xr EVP_EncryptInit 3
.Sh HISTORY
.Fn EVP_CIPHER_CTX_key_length ,
.Fn EVP_CIPHER_key_length ,
.Fn EVP_CIPHER_CTX_iv_length ,
and
.Fn EVP_CIPHER_iv_length
first appeared in SSLeay 0.6.5 and have been available since
.Ox 2.4 .
.Pp
.Fn EVP_CIPHER_CTX_ctrl
and
.Fn EVP_CIPHER_CTX_set_key_length
first appeared in OpenSSL 0.9.6 and have been available since
.Ox 2.9 .
.Pp
.Fn EVP_CIPHER_CTX_set_padding
first appeared in OpenSSL 0.9.7 and has been available since
.Ox 3.2 .
.Pp
.Fn EVP_CIPHER_CTX_set_iv
and
.Fn EVP_CIPHER_CTX_get_iv
first appeared in LibreSSL 2.8.1 and have been available since
.Ox 6.4 .
.Sh BUGS
.Dv EVP_MAX_KEY_LENGTH
and
.Dv EVP_MAX_IV_LENGTH
only refer to the internal ciphers with default key lengths.
If custom ciphers exceed these values, the results are unpredictable.
This is because it has become standard practice to define a generic key
as a fixed unsigned char array containing
.Dv EVP_MAX_KEY_LENGTH
bytes.
